Power systems in many areas of North America and around the world currently are operating close to limits. Operation under such stress makes the modern power system susceptible to various disturbances. An adaptive emergency control scheme is needed to protect the system from large disturbances. Controlled islanding is one of the more efficient strategies to protect the power system from cascading outages caused by large disturbances.

However, most previous research efforts were demonstrated on either sample power systems or power systems equivalenced to a smaller size in comparison to a large realistic power system. This work is the first to demonstrate the efficacy of the controlled islanding approach to a large realistic power system. The proposed approach is applied to the scenario of the August, 14 ^th, 2003, blackout in the Eastern interconnection of North America. The controlled islanding approach constrains the impact of the large disturbances within islands created and prevents the propagation of the disturbance to the rest of the system thus preventing a total system blackout. It is also shown that the proposed islanding method outperforms other emergency control actions like load shedding only by preventing power system failure due to subsequent N-1 contingencies.

In the approach used in this work, slow coherency based grouping is employed to separate the generators into slowly coherent groups. Based on the grouping obtained, islanding schemes are designed to obtain a minimum load-generation imbalance in each island.

The islanding problem could be analytically formulated as a k-way graph partition problem, the computational cost of which is very expensive. Three simplification rules are then proposed to reduce the size of the power-system-specific graph and accelerate the partitioning. A multilevel Recursive Spectral Bisection (RSB) algorithm is applied to obtain the partitions of the reduced-size graph. The result of the graph partitioning is then mapped back to determine the transmission lines that need to be disconnected to island the system.

The strategy is demonstrated on the WECC system and Eastern interconnection respectively. The demonstrations show that the proposed strategy results in effective islanding schemes with reduced simulation time cost.